Mental chronometry is a measure of cognitive speed and is the actual time taken to process information of different types and degrees of complexity. The basic measurement is the individual's response time (RT) to a visual or auditory stimulus that calls for a particular response, choice or decision.
In order to view visual stimulus accurately a person must use the accommodative system, which changes the shape of the lens in the eye to focus the image on the retina, and the vergence system, which is the system responsible for moving the eyes so that they are properly aimed at the object being viewed. Although both the accommodative and vergence systems are used to view an object, current RT testing does not isolate or stress the vergence system sufficiently.
It is known that many and various screening tests are available to test a subject's vision, hearing, speech, motor, and/or hand and motor coordination, as well as perceptual and cognitive skills. Some of these tests involve complex ideas or include some type of cultural or educational bias making it difficult to administer the same universal test across ages, academic grade level, cultures and groups with minimal degrees of mental processing ability.
Although RT tests appear to be very simple compared to the typical items in psychological tests, they can prove to be of significant value in exposing individual differences related to their sensorimotor, perceptual and cognitive components. Galley & Galley (1999) describe the use of certain features of eye movements as a chronometric method for the study of intelligence quotient (IQ). However, although the method is remarkably simple and efficient, it calls for specialized instrumentation and computer programs.
The King-Devick (KD) test of oculomotility is a tool for evaluation of saccade, or fast movements of the eye, that consists of a series of test cards of numbers or letters. The test cards become progressively more difficult to read due to variability of spacing between the characters. Both errors in reading and speed of reading are included in deriving a score. Apart from being able to recognize and name numbers or letters in a left to right sequence, the test lacks for other, simple and considered important, perceptual and cognitive reading demands. The KD test also does not directly target the vergence system.